Oscillation effect of auxiliary winding in primary side regulated flyback converter

Abstract

In the operation of a primary-side-regulated (PSR) flyback converter, oscillation of the auxiliary winding would degrade the system reliability, as this winding plays an important role. In previous works, the oscillation of the auxiliary winding was thought to be related to the oscillation of the primary winding when the switch is turned off. However, a comprehensive explanation has not been given for this phenomenon. Meanwhile, the oscillation of the auxiliary winding depends not only on the oscillation of the primary winding but also on the conducting size and the layer distribution. Based on a multi-winding model obtained from the physical dimensions, this paper derives a mathematical expression to calculate the relation, in the time domain, between the ringing of the auxiliary winding and primary winding. The analytical results would allow the magnetic windings to be analyzed and optimized because the oscillation of the auxiliary winding is expressed as a function of the winding geometry and position. Besides, the skin and proximity effects as well as the nonlinear core properties are considered in the multi-winding model. An application example is also included. Simulation and experimental results of a single-stage, 16-W PSR flyback converter are given to validate the proposed analysis.